The main production process of ultra-high molecular weight polyethylene fiber is as follows: raw material preparation-twin screw extruder-spinning box-spinneret-extraction-drying-heating drawing-winding and forming.
Folding preparation materials
At present, the preparation methods of raw materials at home and abroad are different, the solvents used are different, and the solid content is also different. Therefore, there is no fixed unified model, and the production equipment varies greatly, and conventional melt spinning does not add solvents. But no matter which method is adopted, the desired effect can be achieved in the end. Because production is continuous, the ratio of raw materials must not fluctuate, and it must always be uniform. Although the increase in solid content is one of the important means to increase the output, the draw ratio also increases, and the overall vehicle speed has to respond faster, which increases the difficulty of operation. The amount of wool produced is significantly higher than that, which is not easy to grasp. However, if the percentage of solid content can be controlled within an appropriate concentration, it is still possible, and it must be done according to one’s own circumstances. Increasing the speed of the metering pump is also one of the effective means to increase the output.
Folding mixing materials
The screw extruder plays the role of conveying, stirring, heating and pressurizing the material. First of all, the slurry before entering the “screw” must be defoamed and must not contain water vapor. The material must be fully kneaded and stirred during the transportation process. The heating temperature of each zone should be set in conjunction with the position of the kneading block on the screw, and a certain conveying pressure should be ensured. The setting of the screw kneading block is very theoretical, and different combinations will have different effects on the mixing of materials.
Folded spinning
The main function of the spinning box is heat preservation; temperature control; evenly distributing materials to each spinning assembly.
Folding spinneret
The material is squeezed into filaments by the metering pump, which is realized by the spinneret. The hole size and the shape of the planing surface of the plate are its important technical parameters. It plays an important role in the molding and tensile properties of the fiber. critical use. The temperature of the spinning box and the spinneret are matched, and the temperature parameters are set by observing the molten state of the spun yarn. But if you want to accurately control, you also need to have some specific technical conditions and practical experience.
Fold extraction
It is mainly to extract and replace a large amount of solvent in the thread to obtain “pure” high-strength polyethylene fiber. The selection of extractant varies from manufacturer to manufacturer, and the production process is also different. So far, it is difficult to find an ideal extractant that is economical, practical, safe and environmentally friendly, has good extraction effects, and is non-toxic and tasteless [in the international community, it is also a long-term problem that cannot be solved].
In the process from spinning to extraction, the filaments are stretched randomly and continuously. From the appearance, they change from thick to thin, from translucent to semi-opaque. The stretchability of the silk is gradually improved, and it has a little “strength”. “. If viewed from the inside of the silk, the molecular structure of the raw material has not changed greatly. The macromolecules are not arranged in a directional arrangement, and they are still in a disordered state. The molecules are wrapped and isolated by a large amount of solvent and cannot form molecular chains. Without the shape of the chain, the silk cannot have real strength. At this time, the inside of the fiber actually looks like a circular tube-shaped network. The molecular particles of polyethylene are in the pipe network. As the fiber continues to stretch and become thinner, the solvent continues to precipitate. The shape of the pipe network From round to long, from comb to dense, the density between material molecules gradually increases, and the arrangement of macromolecules gradually changes from a disordered state to a partially ordered state.
Fold dry
The main purpose of the drying process is to remove and dry the extractant sticking to the strands for drawing purposes. This process seems simple to control, but it is actually more difficult. If the process temperature and tension are slightly improperly controlled, a large number of doubling and stiffening will occur, which will cause the semi-finished tow to be unable to continue processing. The key to the drying temperature and drying length. This process cannot be underestimated, it is directly related to the quality of the post-draft product.
Folding heating draft
The drawing process of UHMWPE fiber is basically the same as that of conventional polyester staple fiber, but the required control precision is quite different. This fiber must adopt a multi-stage drafting method to achieve the characteristics of high strength and high modulus. During each stage of under-drafting, the intermolecular structure changes greatly. With the stretching, the macromolecules are arranged from disorder to order, and the crystallinity gradually increases. Only when the orientation of the macromolecules of the fiber along the fiber axis is increased, the number of macromolecular chains will be increased, and the greater the cohesive force, the higher the strength of the fiber will naturally be. The crystallinity of the fiber is increased, and the initial modulus is also naturally increased. Under the action of resistance to external force, the smaller the elongation of the fiber, the smaller the deformation.
In the process of fiber under-stretching, the under-stretching ratio should be as large as possible. Only by allowing the fiber to have a sudden stretch change, can the orderly orientation and high crystallization of the macromolecules be promoted. The internal crystal of the fiber is formed at the same time as the high degree of orientation, and the crystal transition occurs. Due to the relatively high molecular weight of this fiber and the strong resistance to external forces, it can only be produced by thermal drawing process. Therefore, it is necessary to be equipped with a higher stretching temperature to achieve high drafting. For each level of stretching, the temperature is different. It depends on the state of the thread in the previous process. There is no fixed number, but it must be within the temperature range that the fiber itself can withstand. In production, the temperature generally does not exceed 155 degrees Celsius. Otherwise, there will be stiff wires and stiff wires.
Folding and winding forming
The requirements of wire roll forming: the wire tube has no sag, no burrs, and the tow must be fixed in length and weight. The so-called fixed length and fixed weight are by no means simple terms. The requirements for the length and weight of the tow have a deep connotation, and it is very difficult to accurately grasp it. It is a requirement that all production processes must be normal and stable, and the fiber size can only be guaranteed if it is always uniform. If anyone can truly achieve the technical level of fixed length and fixed weight, whoever has reached the peak in the field of high-strength fibers.
